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Surface emission glass cathode: (a) Optical micrograph of two metal electrodes on a glass-silicon substrate, and (b) schematic cross section of the cathode for the region marked with arrows in (a). The electrodes seen on the left and right sides of (b) are fabricated with a tungsten/aluminum structure that is undercut to form a submicrometer gap between the tungsten layer and the glass surface.
(a) Electrical properties of one of the better cathodes during its first testing, with the inset showing bias voltage and bias current as a function of time. The bias current remains negative after the bias voltage was decreased. (b) Anode current as a function of anode voltage and surface electric field into vacuum. After emission is initiated with a bias voltage of , the bias voltage is held at 0 V and the anode voltage is swept from 200 to .
(a) Schematic cross section, not to scale, of a surface emission cathode. Positions “,” “,” and “” indicate the points on a possible emission path where the electron is in the electrode, on the glass surface under the electrode, and on the glass surface under the anode, respectively. (b) Solid curve is the potential energy of the electron on its emission path, labeled with the corresponding points, , and . The dotted line is potential energy of an electron in vacuum. These curves assume the work function of the W electrode is 2 eV (see Ref. 25).
Schematic cross section of cathode indicating the distribution of charge and electric field as one electrode is biased to 200 V and then grounded, with the other electrode and the silicon substrate both grounded. Diagrams illustrate cathode (a) under initial testing, (b) after several minutes to several hours of operation, and (c) after bias voltage is removed.
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